With the increasing enrichment of terminal equipments in the market, many terminal equipments are equipped with frequency modulation (FM) devices. Under normal circumstances, an antenna of FM is rather long, and a terminal equipment does not provide an antenna especially for an FM device, so a method using an earphone as an FM device antenna is proposed. FIG. 1 is a schematic diagram of a connection relationship between an earphone and an FM device of a terminal equipment in the prior art. To prevent attenuation of an FM signal at an earphone connector, an FM ferrite bead (FB) needs to be serially connected to left and right sound channels and a ground wire of the earphone, so as to isolate the FM signal and ensure sensitivity of the FM device in the terminal equipment.
However, because the ground wire of the earphone is serially connected to the FM ferrite bead, signal backflows of the left and the right sound channels both pass the FM ferrite bead on the ground wire when music is played in the earphone. As a result, crosstalk is generated between the left and the right sound channels, a stereo crosstalk index turns bad, and a stereo effect of sound reproduction is badly affected.